Introduction 

What mystery lies behind those dark, towering walls of water that only spread fear, damage and death? A tsunami is a colossal wave of water that can reach heights ranging from 26 to 32 meters. The recent natural tsunami event that occurred in Eastern Asia has inspired me to produce a simulation experiment of a supermarine tsunami. The difference between the Asian tsunami and my experimental tsunami is that the Asian tsunami was generated by an earthquake and my experimental tsunami is generated by a landslide that occurs above the water.

A supermarine tsunami is generated by a huge mass of land falling into the ocean from a volcanic island. The mass of land will push the water in front of it, creating a huge wave known as a tsunami. The water will then spread out across the whole ocean until it reaches land. Once the tsunami starts reaching shallow water, it will start to speed up. Then, it will form into a colossal wave that will be capable of mass destruction of buildings, trees and lives depending on its size.

A tsunami is one of the most destructive and terrifying natural disasters. Scientists of the University College, London warns that a flank of a volcanic island in the eastern Atlantic could collapse and generate a wave of up to 160 feet high that could swamp the coastlines of the Caribbean. Simon Day of the college’s Hazard Research Center predicts that a huge chunk of La Palma, the most volcanically active island in the Canaries, is unstable and could create a supermarine tsunami wave far larger than any seen in history.  This experiment will provide some insight into how these tragedies are caused.

WHAT ARE TSUNAMIS?

A tsunami (soo-NAH-me), the Japanese word for “harbor wave”, is a series of waves that occur in an ocean or other large bodies of water. Tsunamis are caused by any disturbance that displaces large amounts of water from its equilibrium position. Tsunamis are often caused by an earthquake, a landslide, an exploding volcano or even a meteorite impact.

Tsunamis are often caused by earthquakes that occur on the seafloor or in coastal areas. When earthquakes occur in deep oceans, the seismic sea waves are almost unnoticeable because the wave height may only be twelve inches. When the energy from the earthquake reaches the shallow waters of coastlines, bays, or harbors it forces the water into a giant wave, known as a tsunami. Some tsunamis may reach heights of 100 feet or more. They have extremely long wavelength and period.

When an earthquake occurs, the energy generated travels outward in all directions from the source. This can be seen when a pebble is dropped into a small, still pond. The pebble can represent a meteorite or some other energy source such as a supermarine landslide and the pond represents the ocean. The ripples that travel out in all directions from the point where the pebble hits the water represent the energy that creates a sea wave. The waves become larger as they reach shore where the water is shallower. The deeper the water, the faster and shorter the wave is. The wave can travel as fast as a jet airplane and has the ability to travel across the ocean in less than a day.

Submarine landslides which often accompany large earthquakes and volcanic eruptions under the sea can generate a tsunami. Tsunamis can also be caused by supermarine landslides which disturb the water from above, as the momentum from falling debris is transferred to the water into which it falls. Such tsunamis caused by supermarine landslides often die quickly and are not frequently known to affect coastlines farther away from the source.

Below is a brief description of how tsunamis generated by submarine earthquakes occur.

  Initiation

In submarine earthquakes, the seafloor is “permanently” uplifted and down-dropped. This pushes the water up and down. When the water is pushed above, a strong energy is created and this causes the sea level to be transferred to the horizontal propagation of a tsunami wave. The above diagram illustrates how the initial tsunami happens when an earthquake rupture occurs in relatively deep water.

 Split

Within minutes of the submarine earthquake, the initial tsunami is split into two tsunamis, a distant tsunami and a local tsunami. The distant tsunami travels out to the deep ocean and the other tsunami, the local tsunami travels towards the nearby coast. The speed at which both tsunamis travel varies. The deep ocean or distant tsunami travels faster than the local tsunami near shore. This is because tsunamis travel faster in deeper water. 

 Amplification

As the local tsunami travels over the continental slope, its amplitude increases and its wavelength decreases resulting in steepening of the leading wave. The deep ocean tsunami travels farther than the local tsunami because of the higher propagation speed. As the deep ocean tsunami approaches a distant shore, amplification and shortening of the waves will occur. Just the same happens to the local tsunami and this is shown in the picture above. 

Runup

After the runup, part of the tsunami energy is reflected back to the open ocean. Also, a tsunami can generate edge waves which travel back-and forth, parallel to shore. The effects caused by the edge waves result in many arrivals at a particular point on the coast rather than a single wave. Because of the complicated behavior of tsunami waves near the coast, the first runup of a tsunami is often not the largest of the tsunami waves. This fact makes it important that the public should not return to a beach several hours after a tsunami hits because the tsunami danger is not over after the first wave.